Sendmail and SMTP AUTH

[Alexander Dalloz]

Am Fr, den 09.07.2004 schrieb Rodolfo J. Paiz um 18:26:

> >>>I use define(`SMART_HOST',`[mail.bellsouth.net]') in
> >>>sendmail.mc.  This has been working well since long before FC2.
> >>
> >>Why the Bellsouth SMTP server in squared brackets?
> >
> >I haven't seen that done in SMART_HOST, but in mailertable the square 
> >brackets mean that the host is the actual SMTP host. Without them, 
> >sendmail does a DNS lookup on the name looking for an MX record, assuming 
> >that the name is an email domain, not a particular host.
> 
> So in theory then, when we *know* that a given hostname is the MX record 
> for that domain then we can put its name in brackets and save two DNS lookups?

Yes, for Sendmail you prevent/forbid MX lookups by putting a host
address (name or IP) into squared brackets. But you should be really
sure to which host you "force" it.

> Rodolfo J. Paiz

If you do host lookups you can see that mail.bellsouth.net is not the MX
for mail.bellsouth.net, so probably special mail servers for the own
customers.

$ nslookup mail.bellsouth.net
Server:         192.168.0.1
Address:        192.168.0.1#53
             
Non-authoritative answer:
Name:   mail.bellsouth.net
Address: 205.152.59.16
Name:   mail.bellsouth.net
Address: 205.152.59.17

$ host -t MX mail.bellsouth.net
mail.bellsouth.net mail is handled by 0 mx01.mail.bellsouth.net.
mail.bellsouth.net mail is handled by 0 mx00.mail.bellsouth.net.

;; ADDITIONAL SECTION:
mx00.mail.bellsouth.net. 10377  IN      A       205.152.59.32
mx01.mail.bellsouth.net. 10377  IN      A       205.152.59.33

So the MX hosts for bellsouth.net have different names and IPs than
mail.bellsouth.net.

Alexander


-- 
Alexander Dalloz | Enger, Germany | GPG key 1024D/ED695653 1999-07-13
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